Include global Ember CLI install in setup docs

[pimterry]

Tiny tweak; you need ember-cli installed globally to be able to run the site with the Ember command line runner, just npm install is not enough.

[killercup]

I would very much prefer to instead tell people to use npm start -- --proxy https://staging-crates-io.herokuapp.com (requires npm >2.1 IIRC). This makes use of the already installed local dependency.

[pimterry]

Interesting. NPM 2 is only relatively recent and is a major version bump, so I'm a little cautious about requiring it. It also seems slightly messy that anybody who wants to run a local UI has to specify the proxy themselves though, when that seems like a common case, and I think we can solve these both at once.

I've pushed a commit that adds a startui script to package.json, and updates these docs further to match. This can be run with npm run startui, which works fine in NPM < 2 (tested on 1.4.9, which happens to be what's installed on my work laptop) without global ember-cli, and starts up the server UI backed by the staging site. Anybody who does want to use a specific proxy can upgrade to NPM 2.0 and specify it by hand, but that seems like a far more niche case.

Does that sound reasonable?

[killercup]

Sounds good. I guess that specific case (proxy to the staging system) is what most people who edit the UI want anyway.

[alexcrichton]

Thanks @pimterry!